Paleoclimatologists analyzing sediment cores from an isolated subglacial lake in Antarctica discovered a sharp spike in micro-diamond concentrations in layers corresponding to 12,800 years ago. Because micro-diamonds typically form under the extreme temperatures and pressures generated by hypervelocity cosmic impacts, the researchers concluded that a comet impact caused the abrupt atmospheric cooling event recorded in the sediment layers from that era. Which of the following is an assumption upon which the researchers' argument depends?
- The micro-diamond spike in the sediment layers was not produced by terrestrial geological events, such as deep-mantle volcanic eruptions or tectonic shearing.Answer
- BCosmic impacts occurring 12,800 years ago deposited micro-diamonds exclusively in polar lake basins rather than in lower-latitude landmasses.
- CMicro-diamond concentration is the single most accurate proxy available to paleoclimatologists for determining exact global temperature fluctuations.
- DThe abrupt cooling event recorded in the sediment layers was preceded by a prolonged period of elevated global ocean surface temperatures.
- ESediment samples collected from neighboring Antarctic ice shelves contain lower overall concentrations of cosmic debris than samples from the subglacial lake.
Answer
The argument assumes that the micro-diamond spike in the sediment layers was not produced by terrestrial geological events, such as deep-mantle volcanic eruptions or tectonic shearing.
The conclusion asserts that a comet impact caused the cooling event based solely on the presence of micro-diamonds. For this evidence to lead to that conclusion, the researchers must assume that no alternative, non-impact mechanisms (such as terrestrial volcanic or tectonic forces) produced the micro-diamonds. Negating this statement breaks the logical connection between micro-diamonds and the cometary impact hypothesis.
Step-by-Step Solution
Key Concept
Identifying Necessary Assumptions via the Negation Test